Potassium iodide promoted thiolation of pyrazolones and benzofurans using aryl sulfonyl chlorides as sulfenylation reagents

Abstract

An efficient, transition-metal-free method to synthesize pyrazolone thioethers as well as 2-aryl and 3-aryl benzofuran thioethers by employing aryl sulfonyl chlorides as sulfenylation reagents in the presence of triphenylphosphine was developed. Potassium iodide was found to facilitate the transformation for the first time by generating more reactive sulfenyl iodide in situ from sulfenyl chloride.

Tetrabutylammonium Iodide–Promoted Thiolation of Oxindoles Using Sulfonyl Chlorides as Sulfenylation Reagents

“…Treatment of 3-methylindolin-2-one ( 1a ) with 4-methylbenzenesulfonyl chloride ( 2a ) in the presence of PPh 3 in 1,4-dioxane at 80 °C afforded 3-methyl-3-( p -tolylthio)indolin-2-one ( 3aa) in 56% yield ( Table 1 , Entry 1). In agreement with our previous studies, this transformation was facilitated by iodide anions [ 21 ]. Therefore, a number of classical iodides were initially screened, including potassium iodide (KI), ammonium iodide (NH 4 I), and tetrabutylammonium iodide ( n -Bu 4 NI), with the highest yield observed for n -Bu 4 NI ( Table 1 , Entries 2–4).…”

“…Based on our previous work [ 21 ], a plausible reaction mechanism was proposed ( Scheme 4 ), featuring the initial reduction of sulfonyl chloride 2 by PPh 3 to sulfenyl chloride F via intermediates A – E . F is converted into sulfenyl iodide G in the presence of iodide anions.…”

“…Recently, the use of sulfonyl chlorides as sulfenylation reagents has been reported by You ( Scheme 2 , Equation (1)) [ 19 ], Zheng ( Scheme 2 , Equation (2)) [ 20 ] and our group ( Scheme 2 , Equations (3) and (4)) [ 21 ]. As a part of our on-going development of new sulfenylation methods [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ], we report here a novel tetrabutylammonium iodide-facilitated thiolation of oxindoles with sulfonyl chlorides as sulfenylation reagents ( Scheme 3 ).…”

A walk around the application of nanocatalysts for cross-dehydrogenative coupling of C–H bonds

“…53 Without slight doubt, the most straightforward approach to the synthesis of symmetrical 1,3-diynes is the oxidative homo-coupling of two terminal alkynes, which known as the Glaser coupling. 54 Although numerous efficient metal nanocatalysts have been reported for this interesting and useful reaction (Table 4), [55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70] the nanometal-catalyzed hetero-coupling reactions between two different alkynes were less developed. Noteworthy, due to the competitive reaction pathways between homo-coupling and hetero-coupling reactions, synthesis of unsymmetrical 1,3-diynes is more difficult compared to the symmetrical ones.…”

Sulfenylation of C–H Bonds for C–S Bond Formation under Metal‐Free Conditions

“…In 2016, Lu and co‐workers found that arenesulfonyl chlorides were good sulfenylating reagents for the sulfenylation of pyrazolones and benzofurans . Potassium iodide should be added to facilitate the transformation by generating more reactive sulfenyl iodides in situ from sulfenyl chlorides (Scheme ).…”